An imaging optical system is configured with a first lens group disposed on a first optical axis and capturing a luminous flux from a subject along the first optical axis, a prism that folds the luminous flux passed through the first lens group toward a direction along a second optical axis that is substantially perpendicular to the first optical axis and second to fifth lens groups disposed on the second optical axis. At the end of the operation, while the first lens group is driven in a direction of the prism along the first optical axis, the second to the fourth lens groups are driven to an initial angle of view position where these lens groups are to be present at the start of the operation. Thereby, an imaging apparatus whose chassis is very thin and that can realize a high pixel counter and a large magnification, while enabling the speeding-up of the starting operation and the ending operation, can be provided.